1. Field of the Invention
The present invention relates to a developing station. More particularly, the present invention relates to a developing station having a plurality of air nozzles, in which each nozzle capable of blowing a jet of air onto the back surface of a wafer so that residual developer solution is removed.
2. Description of the Related Art
The fabrication of an integrated circuit (IC) involves a large number of complicated steps. In general, a wafer has to go through hundreds of different steps that require one to two months of processing time before each integrated circuit chip is ready for shipment. Principally, the IC industry is a high-tech industry that entails IC design, wafer fabrication, wafer testing and wafer packaging.
Among the many IC fabrication steps, photolithography is a one of the most critical. A large number of steps that relate to the fabrication of MOS transistors or structures such as film patterning and doping require performance of photolithographic operations. A conventional photolithographic operation can be further divided into stages including coating, exposure and development.
Using photolithographic development as an example, the process involves removing the exposed photoresist from a wafer by chemical means so that a patterned photoresist layer is formed. There are a number of methods for developing photoresist. However, to be in line with conventional photolithographic operation, most commercial developing station employs what is known as the `spray/puddle` method. The spray/puddle method is carried out in three stages. In the first stage, developer is sprayed onto a wafer mounted on a spinner. In the second stage, the wafer remains is a static state for carrying out what is known as puddle development. After development, the wafer is cleaned with water and then dried by spinning.
The aforementioned three-stage process can be entirely completed in the same developing station. FIG. 1 is a schematic cross-sectional view showing a jet-cleaning device within a conventional developing station. As shown in FIG. 1, the developing station includes a spin suction pad 10, a knife ring 12 and an external ring guard 14.
The spin suction pad 10 is used to support the back surface 18 of a wafer 16 so that developer solution can act on the positive wafer surface 20. The spin suction pad 10 has an external diameter smaller than the wafer 16 so that the peripheral portion of wafer back surface 18 is exposed. Since capillary action may result in the flow of developer liquid onto the wafer back surface 18 when the positive surface 20 of the wafer 16 is being developed, the wafer back surface 18 may be contaminated.
To prevent the inversion of liquid and contamination of wafer back surface 18, a plurality of nozzles for emitting water jets 22 are normally installed under the spin suction pad 10. The water jets 22 aim at the back surface 18 so that any back flowing developer liquid may be removed. In order to stop the back flow of water jets mixed with the developer liquid, the suction pad 10 is surrounded by the knife ring 12. An external guard ring is also installed to prevent the sputtering of liquid outside the developing station.
However, the water jets that target the wafer back surface do not form a continuous film of wafer, and cleaning efficiency is rather low. Furthermore, to obtain the optimal cleaning, distance between the knife ring 12 and the wafer back surface 18 must be carefully set. Ideally, the water jets must flow to the edge of the wafer but permit no back flow of the developer liquid. Such an adjustment can be very time-consuming.